1. Field of the Invention
The present invention relates generally to a mechanical tree pruning device. In particular, the present invention relates to a hedge trimmer with a folding pole, which has the capability of operating at unusual heights, twenty (20) feet or more from the ground.
2. Description of the Prior Art
Numerous devices for pruning and trimming hedges from the ground up are known in the prior art. Generally, such devices have a power source, a long pole and a cutting apparatus at the top end of the pole. The power source is typically a combustion engine or an electric motor. The following prior art references are relevant to the field of the present invention.
1. U.S. Pat. No. 2,703,928 issued to Southwick (hereafter the "Southwick Patent").
2. U.S. Pat. No. 4,048,722 issued to Howard (hereafter the "Howard Patent").
3. U.S. Pat. No. 4,654,971 issued to Fettes (hereafter the "Fettes Patent").
4. U.S. Pat. No. 4,760,646 issued to Siegler (hereafter the "Siegler Patent").
5. U.S. Pat. No. 4,991,298 issued to Matre (hereafter the "Matre Patent").
In the prior art, the power transmission is typically a rotating shaft inside a telescoping pole. The length of the pole section of these devices are typically changed by telescoping one pole section into another pole section which includes the drive shaft, or attaching pole sections to each other to obtain the desired length. The disadvantage of these devices are related to the overall weight and particularly the weight of the cutting apparatus at the top end of the telescoping pole section. When the device becomes too heavy to operate, it gets to be uncomfortable and its use will be limited. Another disadvantage is the high cost to manufacture these devices which is not practical for today's consumer market.
It has been established that the telescoping pole is functional for a cable drive. However, it requires a storage system for the cable, which consist of several parts and adds weight and cost to the device. With a telescoping pole, the biasing spring load must be adjusted whenever the pole length is adjusted so that the spring can cope with the acceleration forces of the mechanism. It is typical for all pole type tree pruning devices to establish the adjustment to a low limit representing a practical transport and package length. The length is approximately 6 to 7 feet and various other factors limit the practical extended length from 11 to 14 feet. By adding to the extended length the operators proportions and arm position, the reach of the cutting head may be as high as 20 feet. The length of the telescoping poles can be changed by unlocking the telescoping pole members to extend the device to the desired length and re-locking the telescoping pole members.
The Siegler Patent is a spring biased mechanical cable drive. It is a cranking mechanism which creates a reciprocating motion in the cable and two guide rollers guide the cable between the pole entrance and the crank mechanism. It has a rotary action hedge trimmer attachment to the cutting head. The advantage of this approach is that it increases the use of the machine for various purposes. The disadvantage is that it is time consuming to convert the device from one use to the other and back. In addition, the weight of the device is heavy and the main body of the cutting head must cope with chain saw forces.
It is desirable to make the cutting head light in weight, and locate the power source at ground level next to the operator. Because the cutting head and the power source are at least ten (10) feet apart the efficiency and weight of the transmission means is important.